Apparatus for the vaporisation of metals or metalloids



Nov. 10,1970 wjmK'ER 3,539,769

I APPARATUS FOR THE VAPORISATION OF METALS OR METALLOIDS I Filed Sept. 29, 1967 2 Sheets-Sheet 1 D y/V/j BA KHER INVENTOR BY l ' ATTORNEY Nov. 10, 1970 D. w. BARKER APPARATUS FOR THE VAPORISATION OF METALS OR METALLOIDS 2 Sheets-Sheet 2 Filed Sept. 29, 1967 DEA/N15 W. BARKER INVENTOR ATTORNEY United States Patent 3,539,769 APPARATUS FOR THE VAPORISATION OF METALS OR METALLOIDS Dennis Walter Barker, Horsham, Sussex, England, as-

signor to Edwards High Vacuum International Limited, Crawley, Sussex, England Filed Sept. 29, 1967, Ser. No. 671,771 Claims priority, application Great Britain, Sept. 30, 1966, 43,845/ 66 Int. Cl. C23c 13/00 U.S. Cl. 219-275 11 Claims ABSTRACT OF THE DISCLOSURE A vaporisation source for the vaporisation of metals or metalloids including an evaporator base onto which the material to be vaporised may be fed and a radiator heater element which is formed with a cavity across which the evaporator base is supported. The evaporator base and the heater element are both suitable for connection as electrical resistance heaters so that the evaporator base is heated both by its own function as a resistance heater and by radiation from the walls of the cavity.

This invention relates to apparatus for the vaporisation of metals or metalloids and, more particularly, is concerned with the form of evaporator source and the heating thereof.

The type of apparatus contemplated is that for vaporising metals or metalloids on a continuous basis under vacuum for the purpose of depositing films on stationary or moving articles, such as plastics materials, metal sheets, paper, etc.

According to the present invention a vaporisation source for the vaporisation of metals and metalloids comprises a radiator heater element having a cavity therein and an electrically conductive evaporator base supported within or over the cavity for being heated in part at least by radiation from the interior surfaces of the cavity, the evaporator base being adapted for passing an electric current therethrough whereby it serves as an electrical resistance heater.

The evaporator base may have a main region onto which the material may be fed and which is supported over or within the cavity, and two end or side regions in electrical contact with and supported by the radiator heater element.

Further according to the invention a method of heating a vaporisation source comprises the steps of placing an electrically conductive evaporator over a cavity formed in a radiator heater element, heating said radiator heater element so that the evaporator base is heated at least in part by radiation from the interior surfaces of the cavity, and passing an electric current through the evaporator base for internal electrical resistance heating thereof.

Preferably the evaporator base comprises a composite sintered product of titanium diboride and boron nitride.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 shows a source constructed in accordance with the invention and before assembly, the heater element being shown in a longitudinal crosssection,

FIG. 2 shows a longitudinal cross-sectional view of a second source in accordance with the invention, and

FIG. 3 shows a perspective view of the source of FIG. 1 clamped for connection to an electrical supply.

Referring now to FIG. 1, a vaporisation source is shown to comprise a heater radiator element 1 and a shaped evaporator base 2. The heater element 1 is provided with slots 3 which support end portions 4 of the evaporator base, whereby the central portion of the base spans a cavity 5. The base 2 may thus be accommodated by slots 3 which give good electrical connection with the heater 1. This particular arrangement is only shown by way of example and there are clearly many similar source constructions, one of which is shown in FIG. 2. The construction of FIG. 2 differs from that already described in that the shapes employed are all basically rectangular, the cavity 5' being box-shaped and the evaporator base 2 having a rectangular cross-section of constant area along its entire length.

The basis of the invention is that the evaporator base can be used as an electrical resistance heater, and that heat from the heater element is radiated from the walls of the cavity to the evaporator base. In the embodiments shown, being of the preferred type, the evaporator base is actually in electrical contact with the radiator heater element, which simplifies the problems involved if the heater and base were to be energised separately. The base is also supported by the heater. The result of simultaneously heating the evaporator base by electrical resistance heating and by radiant heat from the heater element is to give the following advantages over known arrangements:

(a) a greater thermal efiiciency, that is more vaporisation for a given power input,

(b) an increased life of the source in terms of quantity of material evaporated, and

(0) improved electrical contact to the evaporator base.

Some previously known vaporisation sources have employed evaporator bases which combine the heater and base in one. However, these sulfer from the disadvantage that, as the evaporator base tends to be a hard composite material which has to be resistant to attack from the metal or metalloid being vaporised, the electrical connections to the current supply have to be made directly with the base. Due to the hardness of the base material, good electrical connection is only obtained by positive strong clamping at the terminals which results in distortion, and possible consequent damage, of the base when it expands on heating. However by using a source as provided by the present invention, the heater element may be of a softer material such as graphite, which enables good electrical contact both with the hard material of the evaporator base and with the clamps at relatively low clamping pressures. FIG. 3 shows the source of FIG. 1 with the ends of the heater 1 clamped by clamps 6 with clamping screws 7. The clamps are formed together with water-cooled copper electrodes across which a L.T. supply can be connected. Water inlets 9 and outlets 10 are provided for the cooling water flowing through the electrodes.

A number of suitable evaporator base materials are known to be resistant to attack by molten metals or metalloids, particularly aluminium, and the preferred material used for the base of the present invention is a titaniumboron-nitrogen composite which is a sintered product of titanium diboride and boron nitride. The resistivity of the material can be predetermined by the relative amounts by weight of the TiB and BN in the mixture.

It has been found that under the vacuum conditions at which the vaporisation source of the present invention is required to operate the Ti-B-N composite tends to distort and decompose more rapidly if used above 1600 C. When using a single bar of the composite material for both heater and evaporator base, as outlined above, the bar bows at 1600 C. under these conditions of vacuum thus preventing eflicient use of the evaporating surface. Using the arrangement of the present invention, however, such a disadvantage does not occur and the evaporation rate may be correspondingly increased. It will be noted that the arrangement shown in FIG. 2 illustrates how an existing bar type evaporator source (as mentioned above) can be improved by the addition of a heater element which performed exactly the same task as that shown in FIG. 1.

While the particular forms of evaporation source illustrated are preferred and found to be most suitable, other shapes are clearly within'the scope of the invention. Thus two crucibles, one inside the other, whether they are each in the form of a cylinder or a frustrum of a cone, can be employed, the outer crucible being the radiator heater and the inner one being the evaporator base.

What is claimed is:

1. A vaporisation source for the vaporisation of metals or metalloids comprising in combination an electrically conductive evaporator base having a main region and two support regions and an electrically conductive radiator heater element which is formed with'a cavity therein and has two evaporator base support portions, said two support portions supporting in electrical contact said two support regions of said evaporator base whereby said main region is retained and located within said "cavity.

2. A source according to claim 1 in which said evaporator base comprises a bar shaped and narrowed at the ends to provide said support regions and said radiator heater element is electrically conductive and has recesses to provide said support portions, said recesses receiv'- ing said support regions of said evaporator base in electrical contact.

3. A source according to claim 1 in which said evaporator base comprises a bar of constant rectangular transverse cross-section and said radiator heater element comprises a bar of generally rectangular transverse cross-section having a cavity of elongated cuboidal form and, at either end of said cavity, recesses which define said support portions and receive the ends of said evaporator base, said ends comprising said support regions.

4. A source according to claim 1 in which said evaporator base comprises a composite sintered product of titanium diboride and boron nitride.

5. An evaporator assembly for the vaporisation of metals or metalloids comprising in combination:

(a) an electrically conductive evaporator base having a main region and two support regions,

(b) an electrically conductive radiator heater element which is formed with a cavity therein and has two evaporator base support portions supporting in electrical contact said two support regions of said evaporator base, whereby said main region is retained and located within said cavity, and

() electrical connection means for connecting said heater element to a source of electrical power where by an electric heating current may flow both through said heater element and said evaporator base.

6. An evaporator assembly accordingtoclaim 5 in which said electrical connection means are attached to said heater by means of clamps.

7. An evaporator assembly according to claim 5 in which said evaporator base comprises a composite sintered product of titanium diboride and boron nitride.

8. A vaporisation source for the vaporisation of metals or metalloids comprising in combination:

(a) an electrically conductive evaporator base in the form of a bar shaped and narrowed at its ends to define a narrowed support region at each of said ends; and

(b) a bar shaped electrically conductive radiator heater element formed with a cavity therein and, at opposite ends of said cavity in the direction of elongation of said heater element, two recesses which receive said support regions of said evaporator base in electrical contact therewith.

9. A source according to claim 8, in which said evaporator base comprises a composite sintered product of titanium diboride and boron nitride.

10. A vaporisation source for the vaporisation of metals or metalloids comprising in combination:

(a) an electrically conductive evaporator base in the form of a bar having opposite ends comprising support regions; and

(b) a bar shaped electrically conductive radiator heater element formed with a cavity therein and, at opposite ends of said cavity in the direction of elongation of said heater element, two recesses which receive in electrical contact said support regions of said evaporator base.

11. A method of heating a vaporisation source comprising the steps of:

- (a) placingan electrically conductive evaporator base within a cavity formed in an electrically conductive radiator heater element, the evaporator base having a main evaporator regionand two support regions which are supported in electrical contact by said heater element,

(b) connecting said radiator heater element to a source of electrical supply, and

(c) passing an electric current from saidsupply through said evaporator base and through said radiator heater element.

References Cited UNITED STATES PATENTS 9/1959 Reichelt et a1 118-49 X 2/1966 Land et al. l17107 X US. (:1. X.R. 118-48; 219-420, 426, 427

11/1956 Holland 219-275 X. 

